Letter

Nature 449, 438-442 (27 September 2007) | doi:10.1038/nature06124; Received 18 April 2007; Accepted 25 July 2007

Coherent quantum state storage and transfer between two phase qubits via a resonant cavity

Mika A. Sillanpää1, Jae I. Park1 & Raymond W. Simmonds1

  1. National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA

Correspondence to: Raymond W. Simmonds1 Correspondence and requests for materials should be addressed to R.W.S. (Email: simmonds@boulder.nist.gov).

As with classical information processing, a quantum information processor requires bits (qubits) that can be independently addressed and read out, long-term memory elements to store arbitrary quantum states1, 2, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits3, 4. Superconducting qubits made with scalable microfabrication techniques are a promising candidate for the realization of a large-scale quantum information processor5, 6, 7, 8, 9. Although these systems have successfully passed tests of coherent coupling for up to four qubits10, 11, 12, 13, communication of individual quantum states between superconducting qubits via a quantum bus has not yet been realized. Here, we perform an experiment demonstrating the ability to coherently transfer quantum states between two superconducting Josephson phase qubits through a quantum bus. This quantum bus is a resonant cavity formed by an open-ended superconducting transmission line of length 7mm. After preparing an initial quantum state with the first qubit, this quantum information is transferred and stored as a nonclassical photon state of the resonant cavity, then retrieved later by the second qubit connected to the opposite end of the cavity. Beyond simple state transfer, these results suggest that a high-quality-factor superconducting cavity could also function as a useful short-term memory element. The basic architecture presented here can be expanded, offering the possibility for the coherent interaction of a large number of superconducting qubits.

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